feat: model based theory combination for `grind mbtc` (#8759)

This PR implements model-based theory combination for grind linarith.
Example:
```lean
example [CommRing α] [LinearOrder α] [Ring.IsOrdered α] (f : α → α → α) (x y z : α)
    : z ≤ x → x ≤ 1 → z = 1 → f x y = 2 → f 1 y = 2 := by
  grind
```